Modified events.view_utils.reverse to return an absolute url using
core.urls.build_absolute_uri.  This is helpful for when we issue
alerts without a request object available to construct the absolute
url.  Also updated the corresponding *toDict methods so as to
take advantage of this.

Changing from ISO format to another more readable format for
serialization functions in events/view_utils.py.  Changes for
things like EMObservations, EventLogs, etc.

Added a namespace to include() of superevents part of API. This fixes
an issue where reverse('api-root') was NOT returning the root of the
API but was rather returning /api/superevents/.

We currently aren't filtering superevents for the user in the
request for the web interface search, so we are removing the
(very minor) filtering in the API for the time being.  In the near
future, we will add the full permissions framework in.

We added exception handling for certain create/destroy methods which
involve multiple object creation (log messages and/or tags) and which
may commonly raise errors, like tag creation with invalid characters.
This was done within the superevent viewsets and in the events api.

Adding an optional "purge" for superevent deletion which removes
GroupObjectPermissions and deletes the data.

Adding try/except blocks to destroy views to handle errors in
perform_destroy

If a tag's name has some "uncommon" characters in it, like
parentheses (or probably others), it will cause errors for the
javascript which renders the event pages, since it tries to use
the tag name in the element id for the delete button.  We now require
that tags only use 0-9a-zA-Z_\- in their names. May have to go through
and delete some tags which use them.

First pass at implementing alerts for superevent creation,
update, annotation, labeling, etc.

Prevent users from removing a superevent's preferred event.
They will have to update the superevent to set a new preferred
event instead, then remove the event.

Changes to the eventlog API caused issues for calls to that resource
from within the javascript which populates the event log on the web
view for an event, since the issuer is no longer a dict containing
'username' and 'display_name' keys, but rather just a string
corresponding to the username.

Shortcuts modules were added for the events and superevents apps.
Currently, they just contain 'is_event()' and 'is_superevent()'
methods.

Splitting up much of the alerts functionality and
improving/generalizing it.

Some imports in superevents/serializers.py were moved to
function-level.  This is because several functions from
superevents/utils.py are used in the serializers for
deserialization (object creation), but the serializers are also
used in the alerts app to serialize objects to dicts.  This created
a circular import issue.

We also fix some of the reverses so that they work without a
request object being present.

Activate Django sites app and create a migration which adds the
LIGO.ORG domain name of the GraceDB instance as a Site. This will
be used to build absolute URIs without needed a request object.

Instantiating a new alerts app and moving the alert functionality from
events/alert.py to alerts/old_alert.py. This commit forms a starting
point where the old alert functionality is still in place and we can
rework the alert infrastructure to be more modularized, flexible,
and adapted to superevents.

Now using get_superevent_by_date_id_or_404 to retrieve the superevent
for log creation via the web interface.

Created a web form and API resource for confirming a superevent as
a GW.  Also added and utilized permissions for allowing this action.

Remove commented out code blocks for file handling in
superevents/forms.py.